One is that it uses a spring clutch for chain retention in the rear derailleur instead of the Orbit fluid damper the two higher-tier groupsets use. To keep costs down, there are a couple of features that Rival doesn't have compared to Force and Red.
The entire groupset comes in at just over 3kg, which means Rival is a little on the weighty side and around a couple of hundred grams heavier than the nearest Shimano 105 Di2 competition.
